The present invention relates to servo control systems, and more particularly to means for automatically calibrating response of servos to control signals provided thereto in a system providing positional, but not velocity, feedback.
Control systems are presently available for controlling the motion of flame cutters or other implements in two dimensions so as to, for example, cut a predetermined series of geometric shapes from a plate of metal stock. One control system presently available utilizes positional feedback in order to derive control signals for the servos which control motion of the flame cutters in the two dimensions. The controller reads the present position of the flame cutter, as represented by the positional feedback signals, and then determines the direction in which the flame cutter must travel in order to follow or return to the desired cutting path. Velocity commands are then generated for the several servos to cause the cutter to travel along this path. The accuracy with which the flame cutters may be forced to follow a predetermined path is determined by the feed rate of the flame cutter and the frequency with which the velocity commands of the various servos are updated. This accuracy may be quite good if velocity commands are recalculated very rapidly.
It is desirable that the speed of the flame cutter as it follows the desired path remain uniform, since the characteristics of the cut are dependent upon the velocity at which the flame cutter moves. In order to provide a uniform feed rate, the velocity commands provided to the various servos are normalized by the control system so that their vector sum remains constant. This is not a sufficient condition to establish uniform feed rate, however, since the different servos may have different response characteristics. It therefore cannot be presumed that simply because the velocity commands have a uniform vector sum, the servo speeds will similarly have a constant vector sum.